(1) Field of the Invention
The invention relates to a technical method and to a maintenance device for a piece of equipment of a vehicle, and more particularly of an aircraft.
The invention is thus situated in particular in the technical field of on-board maintenance systems, and more specifically maintenance systems for electronic equipment.
(2) Background Art
Conventionally, a manufacturer specifies the lifetime of a piece of equipment, and may then perform tests in order to demonstrate that the lifetime of that equipment meets requirements. For example, the lifetime may be evaluated as a number of flying hours, e.g. 10,000 hours for a rotorcraft.
The equipment of an aircraft is subjected to non-negligible levels of vibration that might cause it to deteriorate. It is therefore appropriate to verify that the vibration is not of a kind that is likely to reduce the lifetime of the equipment. Under such circumstances, vibratory testing is performed on the equipment.
Nevertheless, it will be understood that it is difficult to perform tests for the complete lifetime of the equipment, since a test lasting for 10,000 hours, for example, is difficult to envisage at reasonable cost.
Consequently, the equipment is subjected to a vibratory spectrum greater than the vibratory spectrum to which the equipment is subjected in use, but for a duration that is shorter than the predicted lifetime for the equipment.
During a definition stage, a piece of equipment may be thus be subjected to an accelerated and destructive vibration test representing the stresses applied to the equipment during its specified lifetime.
The vibratory spectrum applied during such a test and the duration of the test are obtained by conventional methods, e.g. associating a duration with a vibratory level.
Furthermore, a vehicle, and in particular an aircraft, may be provided with active and passive anti-vibration systems. The vibratory spectrum to which a piece of equipment is subjected is thus determined by taking into consideration the use of such anti-vibration systems.
These anti-vibration systems are designed to present a very high level of reliability. Nevertheless, failure is not impossible, even if extremely rare.
Consequently, in the event of a failure of an anti-vibration system, a piece of equipment may be subjected to non-standard levels of vibration. The damage to the equipment may be increased significantly, e.g. by a factor of ten.
However, such levels of vibration are not always taken into consideration during the equipment definition stage, because of their improbability. Thus, when the vibratory level to which the equipment is subjected becomes increased over a non-negligible length of time, that gives rise to a decrease in the potential lifetime of the equipment.
It can be understood that this gives rise to a problem about the lifetime of pieces of equipment subjected to undue levels of vibratory stress, and to how to perform predictive maintenance on the equipment.
Systems are known that are based on “sentinels” that act in real time to measure the vibratory levels of pieces of equipment, and in particular of electronic cards. Those systems act in real time to measure the vibration to which a piece of equipment has been subjected and to deduce therefrom the remaining lifetime for that equipment.
Such systems are most advantageous, but they present cost that is not negligible.
Thus, document EP 0 541 277 describes an integrated vibration-reducing and structural health monitoring system. Maintenance tools with maintenance actions for performing on equipment as a function of its deterioration are provided, e.g. for a helicopter. Vibration reduction makes use of determining operation under a normal mode or a degraded mode.
Document XP 55016804 entitled, “Airframe loads & usage monitoring of the CH-47D ‘Chinook’ helicopter of the Royal Netherlands Air Force,” A. Oldersma et al., published by the National Aerospace Laboratory, (Jun. 2011), describes working loads on structural frames and verification practices in a helicopter. Flying regimes are recognized in order to adjust how the actual wear of components is determined. Relative component operating durations are provided depending on speeds and various operating situations to which fatigue damage rates are associated.
These relative durations refer to percentages of a lifetime.